It is well known to transfer rivets in tubes with the help of compressed air. The rivets are arranged in a column in the tube which guides them and the compressed air is admitted at one end thereof in order to displace the entire column and thus bring about the expulsion of the rivets, one after another, at the other end of the tube. The essential advantages of such a system reside in the simplicity and in the fact that it permits a distribution of each rivet in a defined position, ready for feeding to an automatic machine.
However, this transfer process only gives satisfactory results if the rivets are in very small numbers in the tube. In effect, when this number increases beyond several units, a blocking of the assembly develops, due to the cumulative effects of mechanical and pneumatic jamming of each rivet in the tube, each rivet functioning as a piston in a cylinder. This phenomenon results regardless of the pneumatic pressure used, because if a rise in the pressure increases the pressure on the column of rivets, it also increases equally the effect of jamming of each rivet, such that a rise in pressure, even substantial, does not permit in practice significantly increasing the number of rivets which may be arranged in the distribution tube. As a result, such a process of distribution is actually useable for transferring rivets to the unit or in a small number from one point to another, but not for permitting distribution of the rivets from a tube in which they will be initially arranged in large numbers. This limitation has practial capital consequences: the actual process is not compatible with a storage of rivets in great numbers in the distribution tube and assumes a feeding from the inlet in proportion to the transfer (the initial distribution means then are provided upstream of the tube). Under these conditions, the process of pneumatic transfer through tubes which is actually known resolves the problem of transporting the rivets from one point to another, (or more generally pieces with a symmetry of revolution about an axis) but not the problem of their storage and sequential distribution at the point of use.
British patent 2,067,149 and German patent 3,148,990 describe a pneumatic distribution process for screws of a particular type ("self-piercing nuts"), but the process is limited to this specific type of piece.
The present invention proposes to remedy the limitations of known processes for distribution of rivets, or more generally, distribution of pieces having a symmetry of revolution about an axis, in order to present each piece with its axis aligned in a given direction.
An essential object of the invention is to permit causing the circulation of a very large number of these types of pieces (theoretically without limit) for bringing them to be presented one by one, with their axis in an appropriate position at the inlet of a tool or a machine where they are to be used, for example a riveting machine in the case of rivets.
Another object is to resolve the problem of storage of said pieces, while permitting the distribution tube to function as the conditioning tube therefor.
Another object associated with the preceding one is to permit an improvement of the homogeneity of the pieces distributed due to a great security of storage (complete absence of manipulation by hand on the stored lot from the storage operation to the piece distribution operation).